Process of making ammonium phosphate.



F. S. WASHBURN.

PROCESS OF MAKING AMMOMUM PHOSPHATE.

APPLICATION man AUG.I7, 1915 1,167,788. Patented Jan. 11, 1916.

F5. Was/2 bum, im-knew UNITED STATES PATENT OFFICE.

FRANK S. WASHBURN, OF NASHVILLE, TENNESSEE, ASSIGNOR, BY MESNE ASSIGN- MENTS, TO AMMO-P HOS CORPORATION, A CORPORATION OF NEW YORK.

PROCESS OF MAKING AMMONIUM PHOSPHATE.

Specification of Letters Patent.

Patented Jan. 11, 1916.

Application filed August 17, 1915. Serial No. 45,924.

To all whom it may concern:

Be it known that I, FRANK S. IVAsHBURN, a citizen of the United States, residing at Nashville, in the county of Davidson and State of Tennessee, have invented certain new and useful Improvements in Processes of Making Ammonium Phosphate; and I do hereby declare the following to be a full, clear, and exact description of the invention, such as will enable others skilled in the art to which it appcrtains to make and use the same.

This invention relates to a process of making ammonium phosphate especially adapted for fertilizer purposes from phosphate rock, and has for its object to provide a process which will be more eflicient and less costly than those heretofore proposed.

With these and other objects in view the invention consists in the novel step and 001m binations of steps constituting my invention, all as will be more fully hereinafter disclosed and particularly pointed out in the claims.

Referring to the accompanying drawing forming a part of this specification in which the figure is a diagrammatic illustration of one form of apparatus suitable for carrying out my process, 1 indicates suitable dissolving tanks for treating fine] 1 divided phosphate rock with sulfuric acid; 2 a filter press for separating the phosphoric acid solution from the insoluble residue; 3 a discharge pipe from the filter press 2 into the acid heating tank or system 6, and 4 represents any suitable escape pipe for steam from said system.

5 indicates an acid circulating pump connected to the acid heating system 6 as shown, and 11 a pipe for conducting hot acid to the first ammoniating tower 9, while 10 represents a pipe conducting unabsorbed am monia vapor and gases to a second ammoniating tower 8 connected to the acid heating system 6 by the steam conducting pipe 7.

13 represents an inlet for a mixture of steam and ammonia fed to the first tower 9; and 12 a pipe connecting the fresh acid tank 25 with the adjusting tank 14 adapted to receive super-ammoniated acid from the tower 9.

15, 16 and 17 represent a triple effect evaporator the elements being connected as shown, and 18 a pump connected to the effeet 17 by the pipe 26 and to the effect 15 by the pipe 27 as illustrated.

19 and 20 represent alternate receivers for the fused liquid under a high vacuum, while 21 represents a surface condenser and 22 a vacuum pump connected as shown.

In order that my process may be clearly understood it is said: I start with finely ground phosphate rock in tank 1, and add sufficient sulfuric acid to the same to convert all of the tri-calcium phosphate into calcium sulfate and free phosphoric acid, and dissolve the impurities in the rock, by adding an additional amount of sulfuric acid. If it is desired to produce this phosphoric acid in a dilute form. the quantity of sulfuric acid to be added need only be sufficient to dissolve the impurities present and convert the tri-calcium phosphate into phosphoric acid, but if it is desired to obtain a phosphoric acid in a concentrated solution, containing say as much as 25% P 0, then one must add a slight excess of sulfuric acid in order to take care of the well known chemical phenomena of mass action, which is found to play an increasingly important part in the reaction as the concentration of phosphoric acid in the solution increases. For instance, if one wishes to obtain a 20% P 0, solution it is necessary to have in this soiution a few tenths of a per cent. of free sulfuric acid in order to obtain a high efficiency of extraction, while if one wishes to work to as high as 25% P 0, in the extracted phosphoric acid, then this solution should contain nearly 1% of free sulfuric acid to obtain a high extraction of phosphoric acid from the rock. I next separate this solution of phosphoric acid from the calcium sulfate and other impurities by filtration as by passing it through the filter press 2, and washing it and I thereby obtain a clear solution of crude phosphoric acid containing only a few tenths of a per cent. of such impurities as iron, alumina and soluble lime, with a slight amount of free sulfuric acid, as above explained. This said clear solution is led from the filter 2 by means of the pipe 3 to the tank, or heating system 6. I may ammoniate this crude solution of phosphoric acid in any suitable manner such as by adding aqua ammonia thereto or by passing ammonia gas into the same. But I prefer to use the ammonia vapor made from commercial calcium cyanamid or lime nitrogen, which contains large quantities of steam at a high temperature. Toaccomplish this I fill the towers 8 and 9 with chemical brick, and feed the crude phosphoric acid from the tank into the tower 9 by means of the pipe 11, while the said hot mixture of ammonia and steam as it comes from the cyanamid antoclaves is admitted through the pipe 13. Any unabsorbed gases or vapors in the tank 9 are led from the top thereof to the bottom of tank 8 by means of the pipe 10, while from the top of said tank 8 the pipe 7 leads any unabsorbed gases or vapors into the acid heating system or tank 6 to warm up the acid solution before it reaches tank 9. In the first tower 9 fed with ammonia, I so regulate the phosphoric acid that when it leaves at the bottom it is transformed into a mixture of mono-ammonium and diammonium phosphates, with as much of the latter as I can possibly obtain; in other words, in this tower I have a fairly large excess of ammonia. Into the second tower 8, which I use merely as a washing tower tor clearing up the ammonia escaped from the first tower, I pass through the pipe 23 a large excess of phosphoric acid, so as to be certain to entrap all the last traces of ammonia. In this way I condense no steam in the systern, allow no ammonia to escape unabsorbed. and at the same time make an emmonium phosphate solution quite high in di-anunonium phosphate. This ammonium phosphate solution I then run into the adjusting tank 14, through the pipe 31, and then add sufiicient phosphoric acid to ex actly neutralize it to the mono-ammonium phosphate stage.

The process of neutralization of this solution I have found involves some complications inasmuch as methyl orange the usual indicator, which has always been used for this work, does not indicate exact neutrality, but possesses a. lag in its indications; so that if one were to operate without corrections, one would not obtain a strictly neutral solution of mono-ammonium phosphate, but would obtain a solution of monoammonium phosphate containing about one fourth of 1% of the phosphoric acid in the di-ammo Ilium form. In the subsequent treatment of the product by this process, I have found that di-ammonium phosphate is decomposed into l110ll0-;lII1l1l021lllIn phosphate, with a consequent loss f ammonia; and, therefore, in order to avoid this loss I find it necessary to correct for this lag of the indicator, by adding a corresponding quantity of phosp oric acid.

I am aware of the fact that there are existing patents calling for the neutralization of phosphoric acid by the use of ammonia, either in excess or to alkalinity. But such neutralized solutions, if treated in the manner hereinafter described, I have found always lose ammonia, and I, therefore, find it necessary to work in the manner just described, if one desires to avoid such losses. I have also discovered that such a solution of mono-aimnonium phosphate possesses rather peculiar properties in regard to its temperature concentration phenomena. That is to say, starting with a. boiling point of something over 100 C. depending upon the initial concentration of the phosphoric acid, and which for a 20% P 1, solution is approximately 102 C. the boiling point slowly rises with an increase in concentration to 105' C. From this point on, the rise is much more rapid with an increase of the concentration than it has been up to the said point until a temperature of 112 C. is reached, at which temperature, it the material is cooled. it will set to a solid mass, though it is still quite liquid when the temperature of 11:2 0. is first reached. I therefore conclude that what happens is the following: The rise in temperature from 102 (I. up to 105 C. is, probably. simply a con centration of the solution; but from 105 upward, there is probably a true fusion of the separated salt in a saturated solution of ammonium phosphate up to a teml'ierattlre of 112 (3., at which point the rest of the water is simply driven off without a rise in temperature. At 112 t. the fused mass contains approximately 10% of water. If heating is continued this water is lost and the material will set in the evaporating ap paratus to a solid mass, which cannot be removed except by a most laborious means. But if this material. is tapped out of the evaporator at 112 G. into a very highly evacuated receiver. the sensible heat in the fused mass is sufficient to evaporate off nearly all of the water the instant the mass is discharged into the high vacuum, and one thus obtains directly from such receiver a product containing only tlflt or 4% of water, and in a granulated form which practically needs no other drying.

A convenient way of carrying out the above process of evaporation involves, therefore, the following steps :I provide a multiple effect evaporator 15, 16, 17 and into the second effect 16 I pump through the pipe 30, the solution of ammonium phosphate from the adjusting tank 14, carrying it as usual to the last. effect of my system through the pipe 29 and pump it back into the first effect 15 through the pipes 26 and 27 which efi'ect 15 I supply with steam at such pressure, by means not shown, that I can readil obtain a. final temperature of the liquid in this said effect 15 of 112 C. or thereabout. I thus obtain in said effect 15 by this system of evaporation a fused product under atmospheric or super-atmospheric pressure; and which product I alternately tap out by means of a suitable valve into the highly evacuated receivers 19 and 20. From these receivers in turn I obtain a dry granular product which of itself is suitable for admixture with most fertilizers or is in such a condition that it can be readily passed through an ordinary drier without danger of adhering to its side walls, and thereby have all its moisture removed, if such is desirable. By this system of operationI have avoided the very great difficulty of drying a highly concentrated and wet solution of ammonium phosphate, such as Would be obtained if ordinary evaporators were used. A product obtained from such ordinary evaporators'would be so wet and adhere so strongly ,to iron that it would be impossible to dry it through any of the ordinary direct fired types of driers within the limits of reasonable costs. y

\Vhat I claim is:

1. The process of treating a crude solution of phosphoric acid with ammonia which consists in providing a supply of said solution; segregating a portion of said solution and subjecting it to the action of a mixture of steam and ammonia; segregating a second portion of said solution of a quantity more than suflicient to absorb any ammonia that may be led to it; and leading the unabsorbed gases and vapors from said first named segregated portion through said second named segregated portion; and leading any uncondensed steam from said second portion to said supply of solution and causing said steam to preheat said supply, substantially as described.

'2. The process of treating a crude solution of phosphoric acid with ammonia .which consists in providing a supply of said solution; segregating a portion of said solution and subjecting it to the action of an excess of ammonia; segregating a second portion of said solution, and subjecting it to a deficiency of ammonia; returning said second portion to said supply for subsequent treatment with an excess of ammonia, substantially as described.

3. The process of treating a crude solution of phosphoric acid, which consists in providing a supply of said solution; segregating a portion of said solution, and subjecting it to the action of steam mixed with ammonia in excess; to produce a solution high in di-ammonium phosphate; passing the unabsorbed ammonia to an excess of a second portion of said solution adapted to react with all of said unabsorbed ammonia to produce a second solution containing only mono-ammonium phosphate; returning said second solution to said supply; and adding to said di-ammonium phosphate solution a quantity of phospheric acid slightly in excess of that required to produce a monoamlnonium phosphate solution free from diammonium phosphate, substantially as described.

In testimony whereof I affix my signature, in presence of two witnesses.

FRANK S. WASHBURN.

\Vitnesses:

Ur. M. SCHUMAN, S. W. MAYS.

the highly evacuated receivers 19 and 20. From these receivers in'turn I obtain a dry granular product which of itself is suitable for admixture with most fertilizers or is in such a condition that it can be readily passed through an ordinary drier without danger of adhering to its side walls, and thereby have all its moisture removed, if such is desirable. By this system of operationl have avoided the very great difliculty of drying a highly concentrated and wet solution of ammonium phosphate, such as would be ob tained if ordinary evaporators were used.

A product obtained from such ordinary evaporators'would be so wet and adhere so strongly to iron that it would be impossible to dry it throughany of the ordinary direct fired types of driers within the limits of rea sonable costs. 4 1

What I claim is:

1. The process of treating a crude solution of phosphoric acid with ammonia which consists in providing a supply of said solution; segregating a portion of said solution and subjecting it to the action of a mixture of steam and ammonia; segregatinga second' portion of said solution of a quantity more than suflicient to absorb any ammonia that may be led to it; and leading the unabsorbed gases and vapors from said first named segregated portion through saidsecond named segregated portion; and leading any uncondensed steam from said second portion to said supply of solution and causing said steam to preheat said supply, substantially as described.

[SEAL] '2. The process of treating a crude solution of phosphoric acid with ammonia which" of ammonia; segregating a second portionof said solution, and subjecting it to a deficiency. of ammonia; returning said second portion to said supply for subsequent treatment with an excess of ammonia, substantially as described.- 1 v 3. The-process of treating a crude solution of phosphoric acid, which consists in providing a supply of said solution; segregating a portion of said solution, and subjecting it to the action of steam mixed with ammonia in excess; to produce a solution high in di-ammonium phosphate; passing the unabsorbed ammonia to an excess of a second portion of said solution adapted to react with all of said unabsorbed ammonia to produce av second solution containing only mono-ammonium phosphate; returning said second solution to said supply; and

adding to said di-ammonium phosphate sof ammonium phosphate solution free from diammonium phosphate; substantially as described. v

In testimony whereof I afiix my signature,

in presence of two witnesses.

FRANK s. WASHBURN.

Witnesses: 1 G. M. SGHUMAN, S. W. MAYs.

It is hereby certified that in Letters Patent No. 1,167,788, granted January 11, 1916, upon the application of Frank S. Washburn, of Nashville, Tennessee, foran improvement in Procesises of- Making Ammonium Phosphate," errors appear in the printed specification requiring correction as follows: Page 2, line 76, for P,P,f road P 0 page 3, line 62, for the word phosphoric read phosphoric; and that the said Letters Patent should be read with these corrections therein that the same'm'ay conform to the record of the case in the Patent Oflice.

Signed and sealed this 15th day of February,sA.. D., 1916. I

R. F. WHITEHEAD, Acting Commissioner of Patents.

It is hereby certified that in Letters Patent No. 1,167,788, granted January 11, 1916, upon the application of Frank S. Washburn, of Nashville, Tennessee, for an improvement in Procesises of Making Ammonium Phosphate, errors appear in the printed specification requiring correction as follows: Page 2, line 76, for P,P

read P 0 page 3, line 62; for the word phospheric read phosphoric; and that the said Letters Patent should be read with these corrections therein that the same may conform to the record of the case in the Patent Oflice.

Signed and sealed this 15th day of February, A. D., 1916.

R. F. WHITEHEAD,

Acting Commissioneof Patents.

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